Introduction: Arduino - Laser Tripwire Alarm System
Hello everyone,
In this instructable, we will be building a laser guided tripwire alarm system using a development board.
Step 1: Parts
Components used in this project:
Development board - SainSmart Leonardo R3
Enclosure - Junction Box
Trip wire - Red Dot Laser Diode
Alarm - Buzzer
Sensor - Photoresistor
Power supply - 9v battery
Wire - Male to Female Breadboard Jumper cable
Resistor - 10k
I used an improvised laser diode that was placed on a breadboard that was powered by a 9V battery. Alternatively, a laser pointer will also work well for this project.
Step 2: Assemble
Using a soldering iron, I made two horizontal holes on the junction box to house the photoresistor.
After threading the photoresistor through the junction box, I glued a piece of plastic around it.
This makes it easier to calibrate the sensor in various lighting conditions.
The positive pin from the loudspeaker connects to pin 13 on the development board.
The negative pin from the loudspeaker connects to pin 11 on the development board.
Step 3: Wiring
The photoresistor connects to the 5v pin on the development board.
The remaining pin connects to the analog 0 pin.
A connection between the analog 0 pin and the ground (GND) pin is also established using a 10k resistor.
Before placing the 9V battery inside the enclosure, I used double sided tape to separate it from the development board.
Step 4: Code
int PR = 0; //Analog 0 to Photoresistor
int Loud = 13; //Pin 13 to Loudspeaker
void setup() {
pinMode(PR, INPUT); //Photoresistor is set as an input
pinMode(13, OUTPUT);
pinMode(11, OUTPUT);
Serial.begin(9600);//set serial monitor at 9600 baud
}
void loop() {
int Read = analogRead(PR);// "Read" reads analog0 data
Serial.println(Read);// Print that data
if (Read < 120) //if the value is less than 120 (this can be modified based on your lighting condition),
{
digitalWrite(Loud, HIGH); //speaker turns on
digitalWrite(11, LOW);
}
else //if the value is greater than 120
{
digitalWrite(Loud, LOW);// speaker will turn it off
digitalWrite(11, LOW);
}
delay(1000);//run every second }
Step 5: Done
Once the sensor is calibrated to your prefered setting, you can upload the code and close the junction box.
This version is is calibrated to work in low light conditions.
Although I used 9V batteries for this project, you can also use 5V wall adapters as a permanent solution.
If you want to see this project in action, please click on the link.

Runner Up in the
Automation Contest 2016
25 Comments
Question 5 years ago on Step 5
Serial monitor is reading that the resistance is changing with the laser however the buzzer isn't making a sound. it is properly connected, do I have a defective buzzer???
5 years ago
Congratulations colleague!!!
6 years ago
Would it be possible to make one with a Raspberry Pi, so you could include some more advanced scripts (txt or email notifications), rather than just the buzzer?
6 years ago
@TX: Perhaps the same Ardy could CW "modulate" the Laser Diode and then discriminate on the detector. Could this prevent he laser pointer spoofing-defeat you mentioned? It may mean that the Laser Diode has to be co-located with the Arduino and then a mirror or reflector would be used at the far end for a round trip . I am thinking of using this with a Nano and BluTooth or ZigBee or even Wifi from the lane to the farmhouse; perhaps even two beam pairs to tell in which direction the vehicle or pedestrian is travelling.
Reply 6 years ago
Rad, that's a good direction to take this author's presentation. I'd encourage you to try it in your shop before you hide all your valuables behind your laser protection "wall." :D
6 years ago
As a simple desktop demonstration, this is a great project for learning.
However, as an author, you owe it to your readers to advise them how ambient light affects your laser triggering.
For instance, what if a "bad guy" shines a flashlight on your sensor and then walks through the area of the beam? Will your alarm sound?
Reply 6 years ago
Please dont make this sound as work by taking all the fun out of it :(
Reply 6 years ago
Be nice, Dennis. No sad faces allowed. :)
There are already people commenting about creating their own property perimeter alarms. Shouldn't the author comment about whether (or how) that would work?
Reply 6 years ago
Well...being an author myself I say if this author thinks its fun to dig in deeper then yes please do. But no strings attached, its a hobby!
6 years ago
convoluted. Terrible directions.
6 years ago
this project may be great for aurdino but a infrared laser ldr,light dependant resistor, and a small pc board and 9v battery is simple. circuita abound foe the circuit to recieve the ir light is simple and cheap without ardino and low cost
6 years ago
Nice!! =D
6 years ago
Very nicely done sir!
6 years ago
Great project, What is the max distance between sensor and laser
Reply 6 years ago
I've seen visually 500 mW red lasers at over 800 feet, so I think with the right calibration (perhaps a variable resistor) you could go that far, and with mirrors you could circle your yard. (Depending of course on if you have a huge yard, build two or three...)
Reply 6 years ago
Just depends how strong your laser is. When just the laser is on see how far it beams out to, then if needed you could also change the code to account for lack of strong light by changing that 120 value in the code to something different to make it more easily read the laser. You'll probably also want to make the photo resistor have more shade around it though.
6 years ago
looks awsome, i would also love to see a silent version
Reply 6 years ago
Or perhaps, put a wired buzzer inside your home for checking the border (perimeter) of your property. I was thinking of a project like this using IR lasers so the "intruder(s)" would not see the laser...
Reply 6 years ago
Remove the buzzer, add a light.
6 years ago
Couldn't you get all these parts from a garage door laser safety unit? Those are cheap to free.